1. Field of Invention
This invention pertains to the art of methods and apparatuses for lawn and garden tractors and more specifically to methods and apparatuses for a lift control and feedback system.
2. Description of the Related Art
It is known for a lawn and garden tractor to have a position feed back control system for use in controlling the position (lifting and lowering) a three point hitch mounted to the back of the tractor. Typically, the position control includes a mechanical linkage that opens and closes a pair of hydraulic valves and allows a lift cylinder to move up and down. Generally, at least for the larger units, at least two important functions are needed. The first requirement is sensitivity, and the second requirement is the ability to lift a large amount of weight (generally 1000 to 1500 pounds or more). The sensitivity is required because the hitch must be capable of gently lowering with nothing on it, i.e. with no load. In the art, these two functional requirements are met by using two separate hydraulic valvesxe2x80x94a first valve used to provide the lifting of loads and a second valve used to proved more xe2x80x9cfine-tunedxe2x80x9d operation such as to provide gently lowering under no load. Therefore, there is a need in the art to develop a feed back control system to accomplish the same two functions with a single control valve.
Typically pulling a lever, which in turn pushes a spool inward to a first position, operates at least one of the pair of control valves. At this position, oil is forced out of a work port to the backside of a lift cylinder. This results in raising the hitch. To lower the hitch, the spool is pushed in the opposite direction, which allows the oil to flow back through the work port and then through an exit line.
The present invention provides a new and improved lift control valve and feedback system, which is simple in design, effective in use, and overcomes the foregoing difficulties and others while providing better and more advantageous overall results.
A control valve and feedback system has three operating states including a lifting state, a neutral state, and a lowering state. The feedback control system comprises a cylinder, a pump, a reservoir for holding working fluid, and a control valve. The control valve comprises a valve body having first and second ends with a bore defined therebetween. The valve body further comprises an inlet port, a return port, a first work port and a second work port. The inlet port, return port, and first and second work ports are defined in the valve body. The inlet port communicates with the bore and the pump. The return port is in fluid communication with the bore and the reservoir. The first work port is also in communication with the bore and the cylinder in the lifting state. The control valve is plumbed backwards so that the first work port and the second work port are in fluid communication in the lowering state. The valve also comprises a check valve disposed in the first work port. The first check valve is adapted to achieve the neutral state and being selectively adjustable to achieve said lowering state. The valve also comprises one spool. The spool is received within the bore and has a first spool section and a cam spool section. The first spool section has a constant diameter, and the spool cam section has a variable diameter. The first spool section is adapted to be utilized with the first check valve to achieve the neutral state. The spool cam section is adapted to be utilized with the first check valve to achieve the lowering state. Accordingly, this invention provides a control valve and feedback system wherein the first check valve is adapted to prevent fluid from entering the associated cylinder during the neutral state.
It is yet another object of the present invention to provide a control valve and feedback system where the check valve is adapted to the selectively opened by a spool cam pin to selectively vary the discharge flow rate of the cylinder.
Further, another object of the present invention is to provide a control valve and feedback system wherein the spool cam pin is disposed in the valve body and contacts an outer surface of the spool cam section.
Another object of the present invention is to provide a lift control valve and feedback system where the check valve comprises a spring attached to the valve body, a ball connected to the spring, and a seat for the ball, where the spring is adapted to bias the ball against the seat and the spool cam pin extends through the seat and selectively contacts the ball as the spool cam pin moves around the spool cam section such that the ball overcomes the bias of the spring.
Still yet, another object of the present invention is to provide a control valve and feedback system that comprises a cylinder port. Where the cylinder is adapted to carry working fluid from the cylinder to the tank and such that the circuit formed between the tank and the cylinder is independent from the return port and the tank.
Further, another object of the present invention is provide a valve where the spool cam section is conical in shape.
It is yet another object of the present invention to provide a controlled valve and feedback system wherein the spool cam section has an angled cross-section that is substantially planar.
Still yet, another object of the present invention is to provide a control valve and feedback system wherein the spool cam section has a curved cross-section.
It is yet another object of the present invention to provide a method of obtaining a lifting state, a neutral, and a lowering state for a hitch of a tractor by using a control valve and feedback system which comprises the steps of positioning the spool to a first position, pressurizing fluid with the pump such that fluid flows from a tank through the inlet port and the first passageway to the cylinder, lifting the hitch, positioning the spool in the second position such that the spool provides fluid flow from the inlet port to the return port, maintaining the hitch in the lifting state, positioning the spool to a third position, draining fluid from the cylinder to the tank through the cylinder port, and lowering the switch.
Another object of the present invention is to provide a lift control valve and feedback system adapted to be used on a tractor that uses a hydraulic lift cylinder to raise and lower implements attached to a three point hitch on the rear of the tractor where a single three-position control valve is designed and piped as with your invention. In this way the hydraulic lift cylinder can accurately lift both relatively heavy and light objects.
Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification.